In U.S. Pat. No. 5,813,343, issued to Harb on Sep. 29, 1998 for PRINTING MEDIA ROLL MOUNTING AND POSITIONING MECHANISM, a device is illustrated for mounting a supply roll of paper into a computer driven printer. The device features an adjustable mounting for different sizes of thermal paper rolls used for printing labels. The device features two, spaced-apart holders or guides for supporting the thermal paper roll. The holders are each mounted on a rack that engages a centralized pinion gear disposed in the paper mounting cavity. Rotation of the pinion gear draws the paper mounting holders toward and away from each other, thus justifying the roll. The spaced-apart holders are biased towards each other, within the paper mounting cavity, by means of a tensioned, coil spring. The spring is attached to a rack supporting one of the paper holders on one distal end, and to the printer frame on the other distal end.
The present invention differs from the above device of the aforementioned patent, in that the paper holders or guides are mounted upon the cover plate or door of the printer. The spring-biased, rack and pinion adjustment mechanism is mounted within the cover plate. A mechanism is attached to the hinge of the cover plate, which locks the paper adjustment guides in place when the cover plate is closed over the internal, paper receiving cavity.
The locking mechanism comprises a hinge pin that fits in the hinge of the cover plate. The hinge pin is fixed to the frame or housing of the printer, and comprises a camming surface. A pawl disposed in the cover plate is engaged by the camming surface of the hinge pin as the cover plate is closed over the paper receiving cavity. The pawl pushes against a second set of racks attached to the supply roll guides. The second set of racks are locking racks that comprise a fine mesh of teeth. The fine mesh of teeth, when mated together, prevents the guides from moving apart with respect to each other. These racks lock the supply roll guides in their paper size adjusted position.